Theorem lt2msqi

Description: The square function on nonnegative reals is strictly monotonic. (Contributed by NM, 3-Aug-1999)

	Ref	Expression
Hypotheses	ltplus1.1	⊢ 𝐴 ∈ ℝ
	prodgt0.2	⊢ 𝐵 ∈ ℝ
Assertion	lt2msqi	⊢ ( ( 0 ≤ 𝐴 ∧ 0 ≤ 𝐵 ) → ( 𝐴 < 𝐵 ↔ ( 𝐴 · 𝐴 ) < ( 𝐵 · 𝐵 ) ) )

Proof

Step	Hyp	Ref	Expression
1		ltplus1.1	⊢ 𝐴 ∈ ℝ
2		prodgt0.2	⊢ 𝐵 ∈ ℝ
3		lt2msq	⊢ ( ( ( 𝐴 ∈ ℝ ∧ 0 ≤ 𝐴 ) ∧ ( 𝐵 ∈ ℝ ∧ 0 ≤ 𝐵 ) ) → ( 𝐴 < 𝐵 ↔ ( 𝐴 · 𝐴 ) < ( 𝐵 · 𝐵 ) ) )
4	2 3	mpanr1	⊢ ( ( ( 𝐴 ∈ ℝ ∧ 0 ≤ 𝐴 ) ∧ 0 ≤ 𝐵 ) → ( 𝐴 < 𝐵 ↔ ( 𝐴 · 𝐴 ) < ( 𝐵 · 𝐵 ) ) )
5	1 4	mpanl1	⊢ ( ( 0 ≤ 𝐴 ∧ 0 ≤ 𝐵 ) → ( 𝐴 < 𝐵 ↔ ( 𝐴 · 𝐴 ) < ( 𝐵 · 𝐵 ) ) )